This invention relates to a process for producing krypton and xenon in which liquid oxygen obtained under rectification by means of an air separation plant is concentrated, and in which krypton and xenon contained in the thus concentrated liquid are recovered safely and efficiently.
In recovering industrially krypton and xenon contained in air, it is a common practice to rectify liquid oxygen which has been separated in a main condenser evaporator of the air separation plant, to concentrate krypton and xenon contained in the rectified liquid to obtain a gas mixture of krypton and xenon, and then to purify and separate the gas mixture, whereby pure krypton and xenon are separately produced. Hydrocarbons included in air are also carried into the liquid oxygen, and are hence concentrated during the concentrating process of krytpon and xenon. The enrichment of the liquid with hydrocarbons, particularly methane is liable to cause explosion. To avoid this explosion hazard, removal of hydrocarbons by adsorption or replacement of oxygen by inert gases such as argon is conventionally carried out. It is however difficult to completely remove hydrocarbons by adsorption. Also, it is insufficient to remove hydrocarbons by using the method of catalitic combustion and adsorption of water and carbon dioxide which are combustion products thereby to eliminate the danger of the explosion of hydrocarbons, because the ratio of the supplied liquid oxygen to the concentrated liquid in the concentrating step should be kept under range of the methane 150-180 in view of explosion limit concentration. In the process replacing oxygen by inert gases such as argon gas, there are disadvantages that an argon extraction system must be provided in the air separation plant, and further that expensive argon is consumed.